1. Field of the Invention
The present invention relates generally to a method for semiconductor substrate processing. More specifically, the invention relates to a method for monitoring and detecting optical emission endpoint(s), for photoresist stripping and removal of residues from a substrate or a film stack on a substrate.
2. Description of the Related Art
As a part of semiconductor manufacturing, various layers of dielectric, semiconducting, and conducting films, such as silicon dioxide, polysilicon, and metal compounds and alloys, are deposited on a silicon substrate. Features are defined in these layers by a process including lithography and etching. Such a process comprises coating a substrate with photoresist, patterning the photoresist, and then transferring this pattern to the underlying layers during etching by using the patterned photoresist as an etch mask. Many of these etch processes leave photoresist and post-etch residues on the substrate and must be removed before performing the next process step.
Patterned photoresist also serves as an ion implant mask for preferentially doping semiconductor substrates in selected areas. The doping or implantation process includes exposing the substrate to ions or an electronic beam of implant species, for example, arsenic (As), boron (B, BF2, BF4), phosphorous (P), indium (In), antimony (Sb) and hydrogen (H). The ion implantation process dehydrogenates the photoresist material, resulting in a hydrogen deficient, carbonized crust layer that is typically one to several thousand angstroms thick on top of the bulk photoresist. This makes the characteristics of the photoresist material vertically non-uniform such that uniform removal (stripping) of the photoresist can be difficult. As such, the photoresist removal process may result in non-uniform removal and substantial post-implant residue remaining on the substrate. Consequently, a technique for monitoring removal of the photoresist is necessary such that the photoresist removal process can be controlled as the characteristics of the material change.
Optical emission spectroscopy is commonly used to detect the endpoint of plasma etch processes. Plasma transitions of reactant or by-product species emit photons which can be detected in the ultraviolet, visible and near-infrared ranges. Thus, the endpoint is usually based on increasing signal for reactants or decreasing signal for by-products. The endpoint is identified when either the reactants or by-products attain a specific concentration (i.e., the respective signals cross a threshold level). However, such an endpoint detection technique does not account for the variations in the characteristics of a photoresist layer that has been exposed to an ion beam.
Therefore, there is a need in the art for a method and apparatus for performing optical emission endpoint detection for photoresist strip and residue removal especially when using a chamber having a remote plasma source.